It is generally accepted that FSH influences spermatogenesis, although the specific sites of hormonal action have not been identified. Recent investigations have demonstrated that FSH is present within the seminiferous tubule. We propose to use the unlabeled antibody, peroxidase-antiperoxidase complex technique of Sternberger, et al. as modified by Moriarty and Halmi to identify anti-FSH binding sites in immature, adult, hypophysectomized and X-irradiated animals. Tissue culture studies will also be conducted on Sertoli cell cultures. Preliminary studies indicate that there is binding in the nuclei of Sertoli cells, endothelial cells of the interstitial blood vessels, and acrosomes and nuclei of spermatids. When anti-hFSH (NIAMDD Batch 3, 1:20,000) was absorbed with 1 ug/ml LH (I-3) or 1 ug/ml TSH (I-1) staining was not significantly reduced. When the same antiserum was absorbed with 10 ng FSH (I-3) staining was abolished. Similarly, when the antiserum was diluted beyond 1:50,000 or when any of the steps were omitted from the staining sequence, staining did not occur. To determine the specificity of the reaction anti-FSH will be absorbed with LH, TSH or FSH using affinity chromatography. Staining will be quantitated by measuring the optical density of electron micrograph negatives. Values will be normalized to compensate for variations in section thickness and photographic procedures. Hypophysectomized (low serum gonadotropin levels) and X-irradiated (high gonadotropin levels) rats will be studied to determine if the staining intensity is a function of the physiological state of the animals. Cultures of Sertoli cells (FSH stimulated and unstimulated) will also be immunocytochemically stained. It is hoped that information resulting from these studies will contribute to our knowledge of the hormonal control of spermatogenesis. This information may be useful in identifying steps in spermatogenesis that are vulnerable to contraceptive procedures and in solving problems of male infertility.